The invention relates to a throttle valve body, especially for an internal combustion engine of a motor vehicle, having a tubular body, which comprises at least an outer casing, an inner casing, a first end face and a second end face, the inner casing forming a flow duct through which a gaseous medium can flow in a main flow direction, a throttle plate fixed to a throttle shaft being swivel-mounted in the flow duct.
Throttle valve bodies are generally used to control the fresh charge quantity of a motor vehicle. Throttle valve bodies comprise a housing with a flow duct and a throttle member arranged in the flow duct. The throttle member assumes a certain position in the flow duct for the admission of a specific fresh charge quantity. For this purpose the throttle member may be mechanically or electronically actuated.
Housings of throttle valve bodies are usually manufactured from plastic or metal. Throttle valve body housings that are made of metal, such as aluminum, can be produced with especial accuracy and may therefore have especially fine tolerances. Fine tolerances are required for a throttle valve body in the area of the throttle plate especially where it is intended that just a very slight movement of the throttle plate should be capable of influencing the quantity of medium flowing through the flow duct of the throttle valve body. In the closing area of the throttle plate these requirements are also termed leakage air requirements.
Metal housings of throttle valve bodies have the disadvantage, however, that after manufacturing of the housing by the die-casting process, for example, expensive finishing of the housing is generally required. Finishing of aluminum housings is necessary, for example, in order to meet the proposed functional requirements in and on the housing. Functional requirements relate, in particular, to the flow duct, the accommodation for the actuator and gear mechanism center distances. Accurate machining of the bearing seats is generally also necessary, since the correct operating clearance (bearing internal clearance) is achieved only by the press fit on the needle-roller bearing.
Throttle valve body housings made of plastic have a lower weight than throttle valve body housings essentially made of metal, such as aluminum. Furthermore, as a material plastic is particularly easy to adapt to widely varying geometric configurations of the housing. In the case of plastic housings manufactured by the injection molding process, inserts such as bearings for supporting the throttle shaft can also be molded into the housing.
Throttle valve body housings made of plastic by the injection molding process have the disadvantage, however, that they shrink during and after the injection molding process. In addition, housings of this type may distort after removal from the mold, that is to say they become deformed when they are taken out of the injection mold. Nor are the dimensions of throttle valve body housings made of plastic particularly stable over an especially wide temperature range. On the one hand throttle valve body housings in a motor vehicle are exposed to outdoor temperatures as low as xe2x88x9240xc2x0 C. On the other hand, in the operation of the throttle valve body the temperature of the throttle valve body may rise to more than 100xc2x0 C. These large temperature fluctuations may lead to detrimental deformations of the plastic in the throttle plate swivel area. These deformations can in turn lead over time to a reduction of the especially high fitting accuracy of the throttle plate in the housing. In this case especially high fitting accuracy means, for example, fitting accuracies of the housing of the throttle valve body in the range from 0 to 30 xcexcm, where the housing is subject to the ISO tolerance in respect of the dimension of the flow duct, for example. As a result of changes in the shape of the flow duct, the especially high leakage air requirements can no longer be met, particularly when the throttle is in the idle position. Associated with this are an increased fuel consumption and a reduced exhaust emission quality. Dimensional stability of the throttle valve body housing, especially the flow duct, over a number of years is therefore necessary for a constant fuel consumption and constant exhaust emission quality.
The object of the invention is therefore to specify a throttle valve body of the aforementioned type, which has an especially low weight and is especially inexpensive to manufacture and the flow duct of which has an especially high dimensional stability under especially high thermal loads. In addition the throttle valve body should be particularly easy to adapt to different installation conditions.
According to the invention this object is achieved in that the outer casing of the tubular body is at least partially enclosed by a plastic housing, at least one actuator for the throttle shaft being arranged in the housing and the tubular body being largely composed of metal.
The invention proceeds on the premise that a throttle valve body, which has an especially low weight and is especially inexpensive to manufacture, the flow duct of the throttle valve body at the same time having an especially high degree of dimensional stability, even under especially high thermal loads, should have a flow duct, which is formed, at least in the area of the throttle plate, by a metal component. This is because metal proves to be particularly dimensionally stable even under especially high thermal loads. Furthermore, metal can generally be machined with more dimensional accuracy than plastic. In addition a metal component can guarantee an especially good thermal connection to electromechanical components such as the actuator of the throttle valve body. Nevertheless, in order to ensure particular ease of manufacture of the throttle valve body, the metal enclosing the flow duct should not require the usual expensive finishing work associated with a throttle valve body housing made of metal. For this reason only the flow duct should be formed from a component made of metal. For an especially low throttle valve body manufacturing cost, the flow duct of the throttle valve body might take the form of a standard metal component. A tubular body, which is available as a standard component, is suitable for this purpose.
In order at the same time to ensure an especially low manufacturing cost for the throttle valve body together with an especially low throttle valve body weight and particular ease of adaptation to different installation conditions, the other elements of the throttle valve body and the tubular body are encapsulated in injection-molded plastic in the manner of a housing. In the process, the plastic housing at least partially encloses the tubular body. The flow duct in this case is formed by the inner casing of the tubular body and is composed of metal. However, recesses or bores may be arranged in the inner casing of the tubular body, through which measuring instruments, for example, come into contact with the flow duct. Said recesses or bores may be sealed with plastic, in order to form a smooth inner casing with the inner casing of the tubular body so as to avoid swirling in the flow duct. The flow duct is then formed not completely but almost completely of metal.
The housing to be molded on can be adapted to specific installation conditions for different throttle valve bodies. The throttle valve body is therefore formed from a uniform standard component, the tubular body, and a differing, specifically adaptable element, the housing to be molded on to the tubular body.
At least the first end face of the tubular body is advantageously enclosed by plastic. The inner casing of the tubular body is thereby protected especially reliably, at least by the first end face, against contamination, which can get into the flow duct from outside.
The outer casing of the tubular body is advantageously enclosed radially all round by the housing. This arrangement of the housing on the tubular body is particularly reliable in ensuring that the tubular body is fixed to the housing.
In addition, a position-sensing device for the throttle shaft is advantageously arranged in the housing. A position-sensing device ensures that the current position of the throttle shaft at any time can be detected and compared with a nominal position for the throttle shaft. This is particularly the case where a control unit is provided in the internal combustion engine of the motor vehicle or in the motor vehicle, to which the current position of the throttle shaft at any given time can be fed and which activates the actuator at least as a function of the nominal position of the throttle shaft, so that the difference between the actual position and the nominal position of the throttle shaft is especially low or ideally zero.
In addition, a return spring system for the throttle shaft is advantageously arranged in the housing. In the event of a failure of the actuator a return spring system causes the throttle shaft with the throttle plate arranged thereon to be brought into a position that generally corresponds to an idling position of the internal combustion engine of the motor vehicle.
The tubular body advantageously has extensions projecting radially from its outer circumferential surface. By means of these extensions the tubular body can be anchored in the plastic housing.
The projections, however, are advantageously intended to accommodate the bearings of the throttle shaft. As a result the bearings are integrated into the mechanical strength of the body. This arrangement of the bearings provides particularly stable support for the throttle shaft in the tubular body.
A metal base plate, which is at least partially enclosed by the housing and is integrally formed with the tubular body, is advantageously provided for the actuator. The actuator is thereby thermally connected to the tubular body. In operation of the throttle valve body the heat generated in the actuator can then pass by way of the connection to the tubular body in the area of the flow duct, where it is dissipated by the gaseous medium passing through the flow duct. In other words, the tubular body at least partially heated by the heat from the actuator is cooled by the medium passing through the flow duct. Moreover, the position of the actuator is predefined when fixing the actuator in the housing, thereby obviating the need for expensive adjustment operations on the actuator.
The tubular body advantageously has a first end area and a second end area, flange eyes being arranged at the first end area, which are integrally formed with the tubular body and are provided with a first connecting tube for connection of the tubular body. Flange eyes integrally formed with the tubular body provide a particularly easy means of connecting the throttle valve body to a first connecting tube, for example, allowing additional fasteners to be dispensed with.
Fasteners, which are integrally formed with the second end area and are intended for connecting the tubular body to a second connecting tube, are advantageously arranged at the second end area. These fasteners are advantageously catches, since with catches the throttle valve body only needs to be snapped into a second connecting tube, for example, and is then firmly connected to the latter.
The housing advantageously has flange eyes, which are integrally formed with the housing and in which a sleeve is advantageously arranged, for connection to the first connecting tube and/or to the second connecting tube. The sleeve may be inserted into the housing mold and then encapsulated by injection molding during manufacture of the housing. A sleeve in a plastic flange eye provides the plastic flange eye with additional stability. This ensures an especially rigid connection of the flange eye to other elements of the internal combustion engine and/or the motor vehicle arranged outside the throttle valve body.
The tubular body is advantageously made of aluminum. Aluminum is particularly easy to work with especially high accuracy.
The tubular body is advantageously formed with an approximately spherical cap shape in the throttle plate swivel area. This area of the throttle is also referred to as the idle area or low-load area. If the tubular body has a spherical cap shape at least in the area of the throttle plate, the characteristic curve of the throttle valve body can thereby be adapted to special requirements. The characteristic curve of a throttle valve body describes the interdependence between the working area or the opening angle of the throttle plate and the mass of gaseous medium that passes through the flow duct of the throttle valve body.
The housing is advantageously sealed by a housing cover, which is fixed to the housing by laser welding. This especially durable connection of the housing to the housing cover is particularly reliable in ensuring that the housing is reliably sealed against external dirt penetration even over an especially long operating period of the throttle valve body. Alternatively, however, the housing cover can also be bonded on to the housing.
The advantages obtained with the invention reside, in particular, in the fact that a standard component such as a tubular body is used in order to take account of widely varying requirements for the so-called xe2x80x9cbodyxe2x80x9d interface, since plastic has hitherto not been suitable for manufacturing all the known interfaces used. Moreover, with a tubular metal body, especially one of aluminum, it is particularly easy to impress widely differing internal contours according to requirements. At the same time metal has an especially high dimensional stability even under extreme thermal loads. At the same time account can be taken of specific throttle valve body requirements with regard to the prevailing installation conditions by varying the plastic shape for the housing. As a result such a throttle valve body is significantly lighter than a conventional throttle valve body made of metal.
The tubular body is therefore a standard component, which is encapsulated by injection molding in a suitable housing for adaptation to different types of motor vehicle. The manufacturing cost of a throttle valve body for a multiplicity of motor vehicles and/or internal combustion engines thereby proves to be particularly low. In this the especially high torsional rigidity of the tubular body made of metal in conjunction with the especially low torsional rigidity of the plastic ensures an especially high degree of dimensional stability for the respective throttle valve body. In particular, any bending of the dimensionally critical body area when fitted on so-called uneven intake manifolds is virtually excluded. At the same time, by virtue of its particularly smooth internal contour, the metal tubular body is particularly reliable in avoiding swirling of the medium flowing in the flow duct.